1. of the Invention
The present invention relates to a method and an apparatus for detecting a sheet thickness in a continuous casting machine, in which a cast piece is continuously cast between a pair of drums.
2. Description of the Prior Art
At first, the prior art will be described with reference to FIG. 3.
In a twin-drum type continuous casting machine, molten metal 3 such as molten steel fed from a tundish 2 is poured into a gap space between a pair of rotating water-cooled drums 1, and after having been cooled, a casting piece 4 is continuously cast. The casting piece 4 is delivered by means of pinch rolls 5 and wound into a coil 6. Reference numeral 7 designates a sheet thickness detector which detects a sheet thickness of the casting piece 4, and the detection signal is used as a feedback signal in a sheet thickness control system. More particularly, while a molten metal level in the tundish is kept constant, a rotational speed of the drum is corrected in accordance with a deviation of the above-described detected value from a target value of the sheet thickness of the casting piece. Practically, the sheet thickness is controlled to have a predetermined sheet thickness by increasing the rotational speed in the event that the really measured sheet thickness is thicker than the target sheet thickness but decreasing the rotational speed in the event that the former is thinner than the latter.
However, the above-described sheet thickness detector in a twin-drum type continuous casting machine in the prior art involved the following problems because of the fact that it was installed behind the drums and it was used for detecting a sheet thickness of a casting piece at a high temperature:
(a) In the case where the drums have been opened due to any troubles during casting, there is a possibility that the sheet thickness detector may be covered by molten metal.
(b) Because of the above-mentioned reason, employment of a sheet thickness detector of radiation type is difficult.
(c) Also, even with respect to sheet thickness detectors of the other types (for instance, a sheet thickness detector of differential transformer type, pneumatic micrometer type, laser type or the like), in the event that they have been covered by molten metal, there is a possibility that they may be damaged.
(d) In the case where the detector is installed behind so as not to be subjected to damage by molten metal if possible, delay in detection becomes large, and a controllability for the sheet thickness becomes poor.